As the information society develops rapidly, the importance of a display device capable of implementing a screen with a sense of reality is being emphasized. For instance, a head-mounted display (HMD) device is being researched.
The HMD device is mainly implemented as safety goggles or a helmet. Once a user wears the HMD device, the user can see a screen in front of his or her eyes. The HMD device has been developed for realization of a sense of virtual reality. A small display such as a liquid crystal display is installed at the HMD device close to a wearer's two eyes, so that images can be projected to the display. Recently, the HMD device is being widely developed for use in a space development center, a reactor building, a military agency and a medical institution, for business use or games, etc.
Thanks to such improvements, smart glasses, one example of the HMD device, are presented on the market. The smart glasses realized as a wearable device conveniently execute functions that are executed in the existing mobile terminal.
However, the smart glasses may have the following problems.
Firstly, the smart glasses have very limited input means unlike other terminals such as a smart phone and a notebook computer. Further, voice input through an input means may not be well-recognized due to external noise. Besides, a wearer's privacy cannot be protected, because a third party may hear the wearer's input voice.